What Is Air Leakage?

Air leakage is the uncontrolled movement of air through gaps, cracks, and openings in a building envelope. In roof assemblies, air leakage allows indoor air to escape and outdoor air to enter unintentionally.

Air leakage differs from ventilation. Ventilation is intentional and controlled, while air leakage is unintended and often uneven.

How Air Leakage Occurs in Roof Assemblies

Roof systems contain numerous joints, penetrations, and transitions that can become pathways for air movement if not properly sealed.

• Gaps at framing connections
• Penetrations for wiring and ventilation
• Discontinuous air barriers
• Attic access points and hatches

Why Air Leakage Matters

Air leakage can transport moisture into roof assemblies, increasing the risk of condensation and material deterioration. It also contributes to heat loss in cold conditions and heat gain in warm conditions.

In many cases, air leakage has a greater impact on energy performance than conductive heat loss alone.

Air Leakage vs Ventilation

Ventilation is a controlled exchange of air designed to manage moisture and temperature. Air leakage is uncontrolled and can undermine the intended performance of ventilation systems.